Lyocell fibres have a tendency to fibrillate during vigorous wet processing such as dyeing. A virtue can be made of this tendency by using procedures which remove the matted, hairy effect produced on the surface of the fabric during dyeing (so-called primary fibrillation) whilst allowing the development of the relatively short surface fibrils (so-called secondary fibrillation) which impart a soft touch to the fabric. This soft touch has been successfully used in casual clothing such as casual shirts, blouses, skirts and trousers, where the surface effect is often known as a peach-touch finish.
For such casual clothing, it has been possible both to dye the lyocell fabric in the length and then make up garments from the dyed fabric and also to make up garments from the undyed fabric and then dye the garments.
For clothing which is required to have a more formal look such as smart shirts and blouses for office wear and smart trousers and skirts, for example with pleats, then the soft-touch lyocell fabric is not so appropriate and a clean, smooth fabric is required. This entails using processing methods which avoid inducing fibrillation of the lyocell fibres.
The conventional route for processing garments having a formal look from lyocell fabric involves dyeing the fabric in open width, for example by a pad-dyeing process, so as to minimise vigorous action on the fabric, and then resinating the fabric with a textile finishing resin such as an N-methylol resin, for example a cyclic resin based on dimethylol dihydroxyethyleneurea (DMDHEU). Additional pre-dyeing steps may include singeing of the fabric, scouring to remove weaving size and causticising, in which sodium hydroxide solution is applied to the fabric to improve its performance against wet creasing. The resin treatment imparts some crease resistance to the fabric and serves to protect the lyocell fibres against fibrillating in later processing.
The dyed and resinated fabric is then cut into shaped panels, which are assembled into garments using conventional methods. The garments may then be given a light wash using a rinse aid and softener before being dried.
Whilst this process route has been used successfully to produce formal-look garments of dyed lyocell fabric, it has disadvantages in that it produces fabrics which are rather stiff and harsh in hand and it requires long production runs for each colour if it is to be economic. Moreover, as is well known, resination of the fabric has a deleterious effect on its abrasion resistance. One proposal for alleviating this fall in abrasion resistance is described in GB 2,322,142 and involves reversing the steps of resinating and causticising the fabric prior to dyeing the fabric. In this proposal, causticising and dyeing are to be carried out on the fabric in rope form in a jet-dyeing machine.
With regard to garment dyeing of lyocell fabric, so far this has been confined to producing soft-touch fabric garments for casual wear, and an undyed garment made from lyocell fabric has not been produced which can retain a formal look through the standard garment dyeing processes.